微空心阴极放电推力器性能研究

微空心阴极放电推力器是一种新颖的电热式微推力器,利用纳卫星提供的1~10 W的功率可提高微推进装置的性能。为了预示该推力器的性能,结合实验中测量的气体温度值和火箭发动机原理,初步计算得出微放电推力器的推力范围为几十至上千μN,以氩气为工质比冲量级为600~1 000 N.s/kg,以氦气为工质比冲量级为3 000 N.s/kg。研究结果表明,微空心阴极放电较小的尺寸结构与强烈并可控的气体加热相结合,可以开发应用在电热式微放电推进中,作为微小卫星,尤其是纳卫星和皮卫星的动力系统。     

Atomistic simulation of kink structure on edge dislocation in bcc iron

Based on the general theory of dislocation and kink, we have constructed the three kink models corresponding to the 1/2 （111）{011} and 1/2 （111）{112} edge dislocations （EDs） in bcc Fe using the molecular dynamics method. We found that the geometric structure of a kink depends on the type of ED and the structural energies of the atom sites in the dislocation core region, as well as the geometric symmetry of the dislocation core and the characteristic of the stacking sequence of atomic plane along the dislocation line. The formation energies and widths of the kinks on the 1/2 （111）{011} and 1/2 （111）{112} EDs are calculated, the formation energies are 0.05eV and 0.04eV, and widths are 6.02b and 6.51b, respectively （b is the magnitude of the Burgers vector）. The small formation energies indicate that the formation of kink in the edge dislocation is very easy in bcc Fe.     

离子推力器工作性能参数控制模型

为了研究离子推力器工作参数对输出特性的影响,通过离子推力器工作性能参数的理论计算公式,建立起离子推力器输入参数与输出参数的Simulink控制模型,根据模型分别对我国研制的30 cm口径以及20 cm口径离子推力器的工作输出参数进行了理论计算,并通过推力测量试验对理论值进行了比对和分析。比对结果表明:在推力理论计算过程中引入二价Xe离子比率和束流密度分布推力修正,以及推力均方误差修正后,推力理论值与实测值符合性较好,计算误差小于1 mN,证明了推力修正方法的合理性。     

An improved EEHEMT model for kink effect on AIGaN/GaN HEMT

In this paper, a new current expression based on both the direct currect （DC） characteristics of the A1GaN/GaN high election mobility transistor （HEMT） and the hyperbolic tangent function tanh is proposed, by which we can describe the kink effect of the A1GaN/GaN HEMT well. Then, an improved EEHEMT model including the proposed current expression is presented. The simulated and measured results of Ⅰ-Ⅴ, S-parameter, and radio frequency （RF） large-signal characteristics are compared for a self-developed on-wafer A1GaN/GaN HEMT with ten gate fingers each being 0.4-μm long and 125-p-m wide （Such an A1GaN/GaN HEMT is denoted as A1GaN/GaN HEMT （10 × 125 μm））. The improved large signal model simulates the Ⅰ-Ⅴ characteristic much more accurately than the original one, and its transconductance and RF characteristics are also in excellent agreement with the measured data.     

多模式离子推力器栅极系统三维粒子模拟仿真

栅极系统是离子推力器推力产生的主要部件,推力器的性能和寿命都与栅极系统密切相关.对于具有多种工作模态的离子推力器,基于电流电压入口的仿真可以有效评估推力器的工作状况.采用三维粒子模拟方法对两栅极系统等离子体输运过程进行了仿真,获得了不同模式下的推力器性能参数,对比NSTAR的在轨测试参数,验证了模型的正确性;分析了工作模式变化对栅极区域电场分布和束流状态的影响以及离子推力器多模式设计需求.分析结果表明:远离栅极系统的外凸型屏栅鞘层和内凹型零等势面、低鞍点电势值和平缓的下游电势分布,有利于提高栅极系统离子通过率,抑制电子返流,减小Pits-and-Grooves腐蚀,是离子推力器工作模式的设计方向;提高束流电压会导致发散角损失增大,但可扩展栅极工作电流范围,在束流强度较大的模式下,使束流具有较好的聚焦状态,有利于减小Barrel腐蚀.研究结果为多模式离子推力器工作模式设计提供了参考.     

<Emphasis Type="Italic">Q</Emphasis> kink of the nonlinear <Emphasis Type="Italic">O</Emphasis>(3) <Emphasis Type="Italic">σ</Emphasis> model involving an explicitly broken symmetry

The (1 + 1)-dimensional nonlinear O(3) σ model involving an explicitly broken symmetry is considered. Sphalerons are known to exist in this model. These sphalerons are of a topological origin and are embedded kinks of the sine-Gordon model. In the case of a compact spatial manifold S ¹, sine-Gordon multikinks exist in the model. It is shown that the model admits a nonstatic generalization of the sine-Gordon kink/multikink, Q kink/multikink. Explicit expressions are obtained for the dependence of the Q kink energy and charge on the phase frequency of rotation. The Q kink is studied for stability, and expressions are obtained for the eigenfunctions and eigenfrequencies of the operator of quadratic fluctuations. It is shown that the Q kink is unstable over the entire admissible frequency range ω ∈ [−1, 1]. The one-loop quantum correction to the static-kink mass is calculated, and the Q-kink zero mode is quantized. It is shown that, in a general static case, the field equations of the model are integrable in quadratures.     

托卡马克中宏观束-等离子体扭曲模不稳定性研究

本文主要研究了具有单一高能离子分量的托卡马克等离子体扭曲模宏观不稳定性。它基本上模拟了中性束平行注入经过电离和电荷交换后在本底等离子体中维持一个稳恒等离子体流的物理过程。高能和本底都用无碰撞的Vlasov等离子体,并取了低频、小拉莫尔半径极限。由于主要考虑束-等离子体无耗散宏观不稳定性,故可用能量原理来分析。结果表明,高能离子束对本底等离子体的外部模没有影响,只影响内部扭曲模的增长率和扰动振幅。对适当选择的速度剖面,束能够完全稳定体系n≥2,m=1模,与Dunlap线性理论结果相反而与目前实验观测一致。m/n=1/1内部扭曲模增长率在所取得模型下随注入能量β_b,注入功率P_bw,轴上安全因子q(0)和束速度的径向剖面分布参数S的不同而出现增稳、减稳及完全稳定的行为。适当选择S,在q(0)<0.924时,高能束能够稳定m/n=1/1模。 关键词：     

A 200-W permanent magnet Hall thruster discharge with graphite channel wall

A 200-W Hall thruster was designed using permanent magnets placing the axial maximum magnetic field outside of the channel, and the anode/gas distributor as an integrated U-shaped structure. A split structure is adopted for the discharge channel to conveniently change the wall material. With the initial conditions that the anode mass flow is maintained at 0.8 mg/s, 1.0 mg/s and 1.2 mg/s over a voltage range of 150–400 V (at 50 V intervals), the discharge properties were determined for the two thruster models with the channel walls composed of graphite and boron nitride (BN). The results demonstrate that under identical operating parameters, the properties of the thruster with the graphite channel walls are similar to the properties of the thruster with the BN channel walls. The maximum difference of the discharge current between the two wall materials is 6.2%; the maximum difference of the thrust and the specific impulse is 3.3%, and that of the anode efficiency is 1.7% (absolute value). These differences are smaller than the corresponding parameter differences observed from changing wall materials in other common Hall thrusters.     

螺旋波等离子体推进器中双层形成的PIC模拟

建立了螺旋波等离子体推进器中双层等离子体形成过程的一维全粒子PIC模型,讨论了放电过程中电子加热模型和等离子体膨胀模型,计算了不同条件下螺旋波等离子体推进器中双层等离子体的分布。结果表明:采用氩气工质,在射频电流90A/m2和工作压强0.05~0.15Pa的条件下,可产生双层等离子体,其密度为1.3×1015~2.8×1015 m-3,双层电势降为10~30V,可加速氩离子束流,喷射速度为3~12km/s,双层加速效应对推进器的性能具有一定影响。     

Fission and Fusion of Solitons for the （1＋1）—Dimensional Kupershmidt Equation

By means of the heat conduction equation and the standard truncated Painleve expansion,the (1 1)-dimensional Kupershmidt equation is solved.Some significant exact multi-soliton solutions are given.Especially,for the interaction of the multi-solitons of the Kupershmidt equation,we find that a single(resonant)kink or bell soliton may be fissioned to several kink or bell solitons,Inversely,several kink or bell solitons may also be fused to one kink or bell soliton.     

Laser-induced fluorescence measurements of velocity within a Hall discharge

The results of a study of laser-induced fluorescence velocimetry of neutral and singly ionized xenon in the plume and interior portions of the acceleration channel of a Hall thruster plasma discharge operating at powers ranging from 250 to 725 W are described. Axial ion and neutral velocity profiles for four discharge voltage conditions (100 V, 160 V, 200 V, 250 V) are measured as are radial ion velocity profiles in the near-field plume. Ion velocity measurements of axial velocity both inside and outside the thruster as well as radial velocity measurements outside the thruster are performed using laser-induced fluorescence with nonresonant signal detection on the xenon ion 5d[4]_7/2–6p[3]_5/2 excitation transition while monitoring the signal from the 6s[2]_3/2–6p[3]_5/2transition. Neutral axial velocity measurements are similarly performed in the interior of the Hall thruster using the 6s[3/2]⁰ ₂–6p[3/2]₂transition with resonance fluorescence collection. Optical access to the interior of the Hall thruster is provided by a 1-mm-wide axial slot in the insulator outer wall. While the majority of the ion velocity measurements used partially saturated fluorescence to improve the signal-to-noise ratio, one radial trace of the ion transition was taken in the linear fluorescence region and yields a xenon ion translational temperature between 400 and 800 K at a location 13 mm into the plume. Received: 27 September 2000 / Revised version: 2 March 2001 / Published online: 9 May 2001     

Fe中刃型位错上扭折及掺杂体系的电子结构

利用离散变分方法和DMol方法,研究了体心立方Fe中1/2［111］（110）刃型位错上扭折及掺杂（N,O）体系的电子结构.能量（杂质偏聚能及格位能）计算结果表明,杂质元素N,O进入扭折芯区的偏聚趋势,这与位错扭折引起的晶格畸变有关.同时,在杂质元素周围有一些电荷聚集,导致扭折上电荷的不均匀分布,杂质原子得到电子,其周围Fe原子失去电子.由于N原子的2p轨道与近邻Fe原子的3d4s4p轨道之间杂化,使N原子与近邻Fe原子间有较强的相互作用,不利于扭折的迁移,使位错运动受阻,有利于材料强度的提高;而O与最近邻Fe原子之间的相互作用较弱.杂质-扭折复合体的局域效应明显影响体系的电子结构、能量及性能. 关键词： 电子结构 刃型位错 扭折 杂质元素     

20 cm口径离子推力器力学特性模拟分析

为了提升20 cm离子推力器的抗冲击性能,对现有结构开展了力学分析和试验验证。对栅极组件进行结构等效处理后,采用有限元方法分析了整机的模态和冲击响应谱。分析结果显示,栅极组件结构等效前后的分析结果对比差距8.3%～11.9%;推力器的3个轴向基频分别为246,248,336 Hz,栅极组件和中间极靴是离子推力器的力学薄弱环节并对整体结构稳定性具有重要影响;在冲击载荷1600 g下,栅极组件表面应力主要集中在小孔区边缘处,且形变也主要发生在小孔区;在采取刚度为1000 kN/m的减振措施后,栅极组件的整体形变位移降低了60%～82%。试验结果显示,在10～1200 Hz的低频扫描过程中,推力器3个轴向的基频分别为256,258,348 Hz,与仿真结果基本一致,采用减振措施后的20 cm口径离子推力器通过了1600 g的冲击试验。     

Kink mass quantum shifts from SUSY quantum mechanics

In this paper a new version of the DHN (Dashen–Hasslacher–Neveu) formula, which is used to compute the one-loop order kink mass correction in (1+1)-dimensional scalar field theory models, is constructed. The new expression is written in terms of the spectral data coming from the supersymmetric partner operator of the second-order small kink fluctuation operator and allows us to compute the kink mass quantum shift in new models for which this calculation was out of reach by means of the old formula.     

Near integrability of kink lattice with higher order interactions

We make use of Manton's analytical method to investigate the force between kinks and anti-kinks at large distances in 1+1 dimensional field theory.The related potential has infinite order corrections of exponential pattern,and the coefficients for each order are determined.These coefficients can also be obtained by solving the equation of the fluctuations around the vacuum.At the lowest order,the kink lattice represents the Toda lattice.With higher order correction terms,the kink lattice can represent one kind of generic Toda lattice.With only two sites,the kink lattice is classically integrable.If the number of sites of the lattice is larger than two,the kink lattice is not integrable but is a near integrable system.We make use of Flaschka's variables to study the Lax pair of the kink lattice.These Flaschka's variables have interesting algebraic relations and non-integrability can be manifested.We also discuss the higher Hamiltonians for the deformed open Toda lattice,which has a similar result to the ordinary deformed Toda.     

AlGaN/GaN高电子迁移率晶体管中kink效应的半经验模型

初步分析了AlGaN/GaN 器件上的kink效应. 在直流模型的基础上, 建立了AlGaN/GaN 高电子迁移率晶体管中kink效应的半经验模型, 并加入了kink效应发生的漏源偏压与栅源偏压的关系. 该模型得出较为准确的模拟结果, 可用来判断kink效应的发生和电流的变化量. 最后, 我们采用模型仿真结合实验分析的方法, 对kink效应进行了一定的物理研究, 结果表明碰撞电离对kink效应的发生有一定的促进作用.     

Dynamics of individual atomic kinks during crystal dissolution

The dynamics of kink motion via atom removal/deposition as a fundamental step in dissolution/crystallization of solids have become directly accessible by a novel scanning tunneling microscopy technique. Results obtained for the electrochemical dissolution of Cu(100) in HCl solution show pronounced local dissolution/redeposition fluctuations at the individual kinks even at the onset of Cu dissolution with average kink propagation and reaction rates in the range 10(3) and 10(5) atoms s(-1), respectively. These experiments allow one to directly measure the central kinetic properties of this electrochemical reaction.     

Approximately straight kink theories

A precise meaning is given to the idea of a kink theory approximating a vectoror vector-bundle-valued theory. It is shown that vector theories taking values in a vector bundle with groupSO(n- s,s;), acting naturally, do not approximate any kink theory. It is further shown that, where a kink theory is approximated by a vector bundle theory, the field equations in the vector theory can give rise to field equations in the kink theory. The theory of Skyrme and the sine-Gordon theory are of this form. An example is given of a nonlinear modification of electromagnetism having solitonlike solutions.     

Gödel Kink Spacetime

A 2+1 version of a rotating perfect fluid spacetime of Gödel type is examined to see whether it has a Finkelstein-Misner kink. It is shown, by three different methods, that the kink number is one.